Theranos, the highly valued blood-testing startup is defending the accuracy of its testing results in the wake of a peer-reviewed study that found they differed widely from those of traditional lab testing companies.

Since its public launch in 2014, the company has promised to revolutionize the lab-test industry with its cutting-edge technology, claiming that it only required a finger prick of blood rather than a venous blood draw to accurately test patients for dozens of biomarkers, including cholesterol and glucose. Those were bold claims, given that blood drops from the same person can differ greatly. But until this week, the public has lacked independent studies to compare Theranos's results to traditional lab companies, such as Quest and LabCorp.

The study, released yesterday in The Journal of Clinical Investigation, found that 12.2% of the results reported by Theranos were outside the expected normal range for healthy people, compared with 7.5% for Quest and 8.3% for LabCorp. Theranos did not come up with an answer to more than 2% of tests, which rarely happens with other labs. 60 healthy patients participated in the study.

It's worth noting that there's usually some variability between labs. But the authors, who hail from the Icahn School of Medicine at Mount Sinai, told the New York Times that Theranos's tests were more outside the normal range than usual, in "ways that would impact clinical decision-making." The results found that Theranos flagged tests outside their normal range 1.6× more often than the other lab-testing services.

In a statement to the press, Theranos responded to the study by referring to the data as "flawed and inaccurate." In its rebuttal, the company's executives made the case that taking a big draw of blood from a vein immediately before a finger prick was not standard practice, and would therefore skew the results. This is not the first time that Theranos has referred to its critics' claims as inaccurate.

But in this case, should we discount the journal's results? I asked a group of geneticists and physicians to weigh in on Theranos's rebuttal via Twitter:

Geneticist Sabah Oney, formerly of biotech giant Roche, pointed out that to Theranos's credit, various factors can affect a sample:

But Mitchell Lunn, a researcher at UCSF, added that some patients with diabetes will receive a finger prick and blood draw in the hospital:

This isn't the first time that Theranos's methods have been questioned. Last year, the Wall Street Journal began publishing a series of stories questioning the accuracy of Theranos's tests.

Shortly thereafter, the U.S. Food and Drug Administration published a heavily redacted report citing concerns that Theranos's specimen-collection vial—its "nanotainer"—had not been approved by regulators. Adding fuel to the fire, the Centers for Medicare and Medicaid Services (CMS), which regulates clinical labs in the United States, reported "serious deficiencies" with one of Theranos's labs in Newark, CA.